Recently, an increasing number of transmission systems and networks take a form in which a WDM or other types of large-capacity transmission system is merged with a transmission apparatus that accommodates many different data services.
Among those transmission systems and networks, devices that use a SONET/SDH transmission method (hereinafter, simply referred to as SONET) are in great demand. This is because an existing SONET transmission apparatus is often utilized in building a transmission system or a network. Another reason is that a protection switch function defined by GR-253, GR 1230, GR 1400, and the like which are standards in SONET is an excellent function indispensable for providing a high quality of service.
A large-scale circuit controlled by a complicated method is necessary to equip a SONET transmission apparatus with the SONET protection switch function. The SONET protection switch function has therefore been implemented by an integrated switch function unit in most cases.
FIG. 40 is a diagram illustrating a configuration example of a SONET/SDH transmission apparatus, which implements a SONET protection method that uses an integrated Time Slot Interchange (TSI) function.
As illustrated in FIG. 40, a SONET transmission apparatus 1 includes a plurality of interface units (hereinafter, also referred to as INF units) 2 that accommodate signals from customers (users), and an integrated TSI/SW control unit 3 connected to the plurality of INF units 2 to perform SONET protection switching.
The INF units 2 each include an optical reception unit 21 that receives an optical signal (main signal) from an optical transmission path (optical fiber), and a framer demultiplexing unit (framer DMUX) 22 connected to the optical reception unit 21. A main signal output from the framer DMUX 22 is sent to the integrated TSI/SW control unit. Each INF unit 2 also includes a framer multiplexing unit (framer MUX) 23 to which a main signal from the integrated TSI/SW controller 3 is input, and an optical transmission unit 24 that sends a main signal to an optical transmission path (optical fiber).
The integrated TSI/SW control unit 3 includes an integrated TSI unit 3A and an integrated switch control unit (integrated SW controller: SW CONT) 3B. The integrated TSI unit 3A includes a reception-side SONET line switch unit (SONET LINE SW) 32 that is connected to the framer DMUX 22 and implements a line switching function, an STS reception pointer unit (STS reception PTR unit) 33 that detects a reception pointer of an STS signal in a main signal on a Synchronous Transport Signal (STS) basis, an STS transmission pointer unit (STS transmission PTR unit) 34 that detects a transmission pointer of a signal on an STS basis, and a transmission-side SONET line switch unit 35. Those SONET line switch unit 32, STS reception pointer unit 33, STS transmission pointer unit 34, and SONET line switch unit 35 are provided for each INF unit 2.
The integrated TSI unit 3A also includes an STS TSI unit 31 (TSI unit 31) to which a plurality of the STS reception pointer units 33 and a plurality of the STS transmission pointer units 34 are connected. The STS TSI unit 31 executes TSI processing (interchanging (sorting) time slots), to thereby perform path switching operation on an STS basis. In other words, the TSI unit 31 performs processing of connecting a signal from each input port to a given output port. Output signals of the TSI unit 31 are connected to the STS transmission PTR units 34.
The integrated SW control unit 3B includes a SW controller 36 that controls the operation of the SONET line switch units 32 and 35, a path alarm overhead processing unit (path ALM OH processor) 37 that performs processing relevant to a path alarm (path alert) detected by the STS reception PTR units 33 and the STS transmission PTR units 34, a TSI controller 39 that controls the TSI processing in the TSI unit 31, and a path switch (path SW) control unit 39 that controls the path switching operation executed by the TSI unit 31.
The SONET transmission apparatus 1 further includes a monitoring controller 41 that monitors the operation of the INF units 2 and integrated TSI/SW control unit 3 described above as an operation monitoring function that targets those components, and a line alarm overhead (line ALM OH) processing unit 42 that corresponds to the framer demultiplexing unit 22 and the framer multiplexing unit 23 in each INF unit 2 and detects a line alarm (line alert).
With the SONET transmission apparatus 1, the number of INF units 2 accommodated that can be mounted in the SONET transmission apparatus 1 (the number of lines accommodated) can be increased by downsizing the INF units 2. Also, line switching and path switching that have a high degree of freedom can be supported by centralizing functions relevant to line switching and path layer switching in the integrated TSI/SW control unit 3.
Patent Document 1: JP 2001-238279 A
Patent Document 2: JP 9-274044 A
In the SONET transmission apparatus illustrated in FIG. 40, the SONET line switch unit (SONET LINE SW) 32 handles high-speed signals. In addition, the SONET transmission apparatus is required to implement a SONET protection switch function that depends on its apparatus configuration. The integrated TSI unit 3A is required for those reasons to be implemented by a dedicated Application Specific Integrated Circuit (ASIC) that depends on the apparatus configuration. The integrated SW control unit 3B, on the other hand, is required to exert switching control on all the INF units 2. The integrated SW control unit 3B which performs this switching control is implemented by a Field Programmable Gate Array (FPGA).
Those can cause an increase in power consumption of the SONET transmission apparatus 1. Also, taking heat generated by the integrated TSI/SW control unit 3 into account may limit the apparatus configuration and where to install the apparatus.
In the SONET transmission apparatus 1, the integrated SW control unit 3B executes switching control of all the INF units 2 and accordingly has a large-scale circuit configuration. The large-scale integrated SW control unit 3B is employed irrespective of the number of accommodated lines of the SONET transmission apparatus 1 (the number of the INF units 2 mounted). When a customer desires a SONET transmission apparatus where the number of lines accommodated is small, this makes the cost of building the SONET transmission apparatus higher than strictly necessary.
Also, SONET protection switching (the integrated TSI unit) is implemented by a dedicated ASIC as mentioned above. This makes it difficult to flexibly deal with a change brought about by adding a function to the integrated TSI unit or enhancing the integrated TSI unit. Adding a function may require developing a new ASIC.
Further, in integrated switch control as the one illustrated in FIG. 40, alarm information about every unit in the SONET transmission apparatus is required to be collected and monitored as alarm information necessary for switch control. The processing scale of this type of collection and monitoring increases in proportion to the number of lines accommodated. Accordingly, implementing a function of collecting and monitoring alarm information may require large-scale ASIC development.